Input match network with RF bypass path

ABSTRACT

A power circuit includes a RF transistor and an input match network coupled to an input to the RF transistor and to an input to the power circuit. The input match network includes a resistor, an inductor and a first capacitor coupled together in series between the input to the RF transistor and a ground, and a second capacitor coupled in parallel with at least the resistor. The value of the second capacitor is selected so that the resistor is bypassed over at least a portion of the high frequency range of the power circuit.

PRIORITY CLAIM

This application is a continuation-in-part of U.S. application Ser. No.13/763,373 filed 8 Feb. 2013, the content of said applicationincorporated herein by reference in its entirety.

FIELD OF TECHNOLOGY

The present application relates to RF (radio frequency) amplifiers, inparticular input match networks for RF amplifiers.

BACKGROUND

RF power amplifiers are used in a variety of applications such as basestations for wireless communication systems etc. The signals amplifiedby the RF power amplifiers often include signals that have a highfrequency modulated carrier having frequencies in the 400 megahertz(MHz) to 4 gigahertz (GHz) range. The baseband signal that modulates thecarrier is typically at a relatively lower frequency and, depending onthe application, can be up to 300 MHz or higher.

RF power amplifiers are designed to provide linear operation withoutdistortion. Input and output impedance matching circuits are used tomatch RF transistors that may have low input and output impedances(e.g., around 1 ohm or less for high power devices), to externaltransmission lines that provide RF signals to and from the RFtransistor. These external transmission lines have characteristicimpedances that are typically 50 ohms but could be any value as decidedby a designer. The input and output matching circuits typically includeinductive and capacitive elements that are used to provide impedancematching between the input and output of the RF power amplifier and theinput and output of the RF transistor. The input and output matchingcircuits provide impedance matching for the signal frequencies that areamplified by the RF power amplifier, such as those in the 400 MHz to 4GHz range.

The use of impedance matching circuits, however, can cause unintendedconsequences that occur outside of the range of signal frequencies thatthe impedance match is being provided for. For example, a typical outputmatch network will include a blocking capacitor for blocking DC. Theblocking capacitor in combination with the RF transistor drain biasinductance creates a low frequency resonance. This low frequencyresonance causes the impedance in the low frequency region to increase.As a result, the frequency response of the RF power amplifier has a lowfrequency gain spike. Such a spike can appear anywhere from a few MHz tohundreds of MHz. The output of a nonlinear operation yields terms withfrequencies at the sum and difference of the original signalfrequencies, plus the original frequencies and multiples of the originalfrequencies, and those multiples are commonly referred to as harmonics.Current wireless signals have high modulation bandwidths. The secondorder distortion components of such wideband signals may fall in theregion of the low frequency gain spike. Further, in most wirelesscommunication applications distortion correction systems such as DPD orDigital Pre-Distortion are used. Such systems model the power amplifier,predict the non-linear performance and adjust the signal characteristicsto reduce the distortion at the PA system output. The undesired highgain (or high impedance) in the baseband region due to the low frequencyresonance negatively impacts the RF transistor and pre-distortionperformance of the overall system.

A resonance in baseband frequency region causes a sharp change in gainat these low frequencies. The frequency at which the low frequency gainpeak occurs is typically known as the video bandwidth of the RF poweramplifier. Moreover, the magnitude of the gain peak also impacts thesystem performance. A higher magnitude of gain peak results in worseoverall system performance. Additionally, the resonance in the basebandfrequency region causes high peak voltages at the drain of RFtransistors such as LDMOS (laterally-diffused metal-oxide semiconductor)transistors. These high peak voltages at the drain of the RF transistorcan surpass the breakdown voltage of the device under certain conditionscausing failures. Consequently, any increase of the gain peak within thelow frequency baseband region can effectively reduce the ruggedness ofthe power device.

SUMMARY

According to an embodiment of a power circuit, the power circuitincludes a RF transistor and an input match network coupled to an inputto the RF transistor and to an input to the power circuit. The inputmatch network includes a resistor, an inductor and a capacitor that arecoupled together in series between the input to the RF transistor and aground. The values of the resistor and the inductor are selected tomatch an input impedance of the RF transistor to a source impedance atthe input to the power circuit over at least a portion of a highfrequency range, wherein the value of the capacitor has a substantiallynegligible contribution to the match at the high frequency range. Thevalue of the capacitor is selected so that the series combination of theresistor, the inductor and the capacitor substantially reduce themagnitude of the impedance presented to the input of the RF transistorin a low frequency range relative to the source impedance at the inputto the power circuit.

According to another embodiment of a power circuit, the power circuitcomprises an RF transistor and an input match network coupled to aninput to the RF transistor and to an input to the power circuit. Theinput match network includes a resistor, an inductor and a firstcapacitor coupled together in series between the input to the RFtransistor and a ground, and a second capacitor coupled in parallel withat least the resistor. The values of the resistor and the inductor areselected to match an input impedance of the RF transistor to a sourceimpedance at the input of the power circuit over at least a portion of ahigh frequency range. The value of the first capacitor is selected sothat the series combination of the resistor, the inductor and the firstcapacitor reduce the magnitude of the impedance presented to the inputof the RF transistor in a low frequency range relative to the sourceimpedance at the input of the power circuit. The value of the secondcapacitor is selected so that the resistor is bypassed over at least aportion of the high frequency range.

According to an embodiment of an RF power amplifier, the RF poweramplifier comprises an input configured to receive a RF signal having aRF signal bandwidth, a LDMOS transistor configured to amplify the RFsignal and an input match network coupled to the input of the RF poweramplifier and a gate of the LDMOS transistor. The input match networkincludes a resistor, an inductor and a first capacitor coupled togetherin series between the input of the RF power amplifier and a ground, anda second capacitor coupled in parallel with at least the resistor. Thevalues of the resistor and the inductor are selected to match animpedance at the gate of the LDMOS transistor to a source impedance atthe input of the RF power amplifier over at least a portion of the RFsignal bandwidth. The value of the first capacitor is selected so thatthe input match network substantially reduces the magnitude of theimpedance presented to the gate of the LDMOS transistor in a basebandfrequency range relative to the source impedance at the input of the RFpower amplifier. The value of the second capacitor is selected so thatthe resistor is bypassed over at least a portion of the RF signalbandwidth.

According to another embodiment of a power circuit, the power circuitcomprises an RF transistor and an input match network coupled to aninput to the RF transistor and to an input to the power circuit. Theinput match network includes a resistor, an inductor and a firstcapacitor coupled together in series between the input to the RFtransistor and a ground, and a second capacitor coupled in parallel withat least the resistor. The value of the resistor is in the milliohmrange, the value of the inductor is in the pH range, the value of thefirst capacitor is in the nF range, and the value of the secondcapacitor is in the pF range.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other. Embodiments are depicted in thedrawings and are detailed in the description which follows.

FIG. 1 illustrates a conventional power circuit.

FIG. 2 illustrates an embodiment of a power circuit.

FIG. 3 illustrates the impedance at the input of the RF transistor as afunction of frequency with the power circuits illustrated in FIG. 1 andFIG. 2.

FIG. 4 illustrates embodiments of the gain response of a power circuitas a function of frequency and blocking capacitor value.

FIG. 5 illustrates embodiments of the gain response of a power circuitas a function of frequency and blocking capacitor value.

FIG. 6 illustrates the gain response peak attenuation as a function offrequency for the power circuits illustrated in FIG. 1 and FIG. 2.

FIG. 7 illustrates another embodiment of a power circuit.

FIG. 8 illustrates yet another embodiment of a power circuit.

DETAILED DESCRIPTION

FIG. 1 illustrates a conventional power circuit 100 that includes a RFtransistor 110, an input match network 120 and an output match network130. Input match network 120 provides impedance matching between inputterminal (IN) and a gate (G) of RF transistor 110, and output matchnetwork 130 provides impedance matching between a drain (D) of RFtransistor 110 and output terminal (OUT). The impedance matching isprovided for a desired RF signal bandwidth (also referred to as the RFregion). The RF region for signals that are amplified by power circuit100 can be in the 400 MHz to 4 GHz range. The RF region for differentapplications can be lower or higher than the aforementioned range.

Input match network 120 includes a matching capacitor C_(IN) having oneterminal coupled to ground. A branch L_(IN2) of the input match network120 is coupled to the other terminal of C_(IN) and to the gate (G) of anRF transistor 110. A branch L_(IN1) couples the input terminal (IN) ofthe power circuit 100 to the terminal of L_(IN2) and the other terminalof C_(IN). The branches L_(IN1) and L_(IN2) of the input match network120 are typically implemented as bond wires, ribbons, etc. The inputmatch network 120 uses selected values for C_(IN) and L_(IN2) to matchan input impedance of RF transistor 110 to the terminal (IN) impedance.In this illustration in FIG. 1, C_(IN)=10 to 100 pF, L_(IN1)=100 to 200pH and L_(IN2)=100 to 200 pH. RF transistor 110 is a LDMOS(laterally-diffused metal-oxide semiconductor) transistor rated at 100Watts. The magnitude of the impedance presented to the gate (G) of RFtransistor 110 is designated by Z_(IN1) and the reference arrowillustrates that this impedance is provided to the gate (G) terminal ofthe RF transistor 110. The impedance Z_(IN1) will be discussed inreference to FIG. 3 and FIG. 6.

The output match network 130 includes a blocking capacitor C_(OUT) and abranch L_(OUT1). L_(OUT1) is coupled to the drain (D) of the RFtransistor 110 and to one terminal of C_(OUT). The other terminal ofC_(OUT) is coupled to ground. A branch L_(OUT2) couples the drain (D) ofRF transistor 110 and one terminal of L_(OUT1) to the terminal (OUT) ofthe power circuit 100. The source (S) of the RF transistor 110 iscoupled to ground. The branches L_(OUT1) and L_(OUT2) of the outputmatch network 130 can be implemented in various different ways such asbond wires, ribbons, etc. The output match network 130 uses C_(OUT) andL_(OUT1) to match an output impedance at the drain (D) of RF transistor110 to a terminal (OUT) impedance within the RF region.

The output match network 130 provides high frequency impedance matchingover the RF region but may also result in an undesirable low frequencygain peak outside of the RF region which corresponds to the lowfrequency resonance. The blocking capacitor C_(OUT) cuts off DC, and thecombination of LC components (e.g., including, but not limited to,inductance from voltage connections external to power circuit 100,branch L_(OUT1) and branch L_(OUT2)) with the DC blocking capacitanceform resonances, resulting in a high gain peak and high peak voltages atthe drain of RF transistor 110 at frequencies in the low frequencybaseband region.

This high gain peak in the baseband frequency region can cause the peakdrain voltage of RF transistor 110 to surpass the breakdown voltage ofthe device under certain conditions, e.g., when unintended systemartifacts appearing in the region of the low frequency gain peak arestrongly amplified, when a baseband component of a broadband signal thatis coincident with the low frequency gain response peak is stronglyamplified by the gain peak, etc. It will be appreciated that thisproblem cannot be completely solved with a more complex matching circuitthat suppresses low frequency signals before they reach the outputterminal, since the excessively high low-frequency signals will still bepresent at the output of the transistor.

FIG. 2 illustrates an embodiment of a power circuit 200. The powercircuit 200 includes a RF transistor 210, an input match network 220 andan output match network 230. Input match network 220 provides impedancematching between input terminal (IN) and a gate (G) of RF transistor210, and output match network 230 provides impedance matching between adrain (D) of RF transistor 210 and output terminal (OUT). The impedancematching is provided for a desired RF signal bandwidth or RF region. Inother embodiments, the impedance matching is provided for at least aportion of a desired RF signal bandwidth or RF region. The RF region forsignals that are amplified by power circuit 200 can be in the 400 MHz to4 GHz range. The RF region for different applications can be lower orhigher than the aforementioned range.

The input match network 220 is coupled between an input inductor L_(IN1)of power circuit 200 and a gate (G) of RF transistor 210. In variousembodiments, the input inductor L_(IN1) is implemented as bond wires,ribbons etc. which couple the input match network 220 to a terminal (IN)of the power circuit 200. In many cases L_(IN1) is a part of the inputmatch network. The output match network 230 is coupled between a drain(D) of RF transistor 210 and an output inductor L_(OUT2) of the powercircuit 200. In various embodiments, the output inductor L_(OUT2) isimplemented as bond wires, ribbons etc. which couple the output matchnetwork 230 to a terminal (OUT) of the power circuit 200. In many casesL_(OUT2) is a part of the output match network. Output match network 230is similar to output match network 130 discussed in reference to FIG. 1.The magnitude of the impedance presented to the gate (G) of RFtransistor 210 is designated by Z_(IN2) and the reference arrowillustrates that this impedance is provided to gate (G) of RF transistor210. The impedance Z_(IN2) will be discussed in reference to FIG. 3 andFIG. 6.

In various embodiments, RF transistor 210 can be a power transistor suchas a MOSFET (metal-oxide semiconductor field-effect transistor), DMOS(double-diffused metal-oxide semiconductor) transistor, GaN HEMT(gallium nitride high electron mobility transistor), GaN MESFET (galliumnitride metal-semiconductor field-effect transistor), LDMOS transistor,etc. and more generally any type of RF transistor device. RF transistor210 and the complete power circuit 200 can be a multi-carrier amplifier,a multiband amplifier, an LTE (long term evolution) compliant amplifier,a WCDMA (wideband code division multiple access) compliant amplifier, an802.11(x) compliant amplifier, etc.

Input match network 220 includes a blocking capacitor C_(IN), aresistance R_(IN) and an inductance L_(IN2). In this embodiment, C_(IN),R_(IN) and L_(IN2) are coupled in series between a gate (G) of RFtransistor 210 and ground. Although the illustrated embodiment showsthis series connection with one terminal of C_(IN) coupled to ground andone terminal of L_(IN2) coupled to a gate (G) of RF transistor 210 withR_(IN) coupled between a second terminal of L_(IN2) and a secondterminal of C_(IN), in other embodiments, C_(IN), R_(IN) and L_(IN2) canbe coupled between ground and gate (G) of RF transistor 210 in othersuitable configurations.

The branch L_(IN2) of input match network 220 can be implemented as bondwires, ribbons, etc. In various embodiments, the branch L_(IN2) can beimplemented as other suitable inductors. The blocking capacitor C_(IN)of the input match network 220 can be implemented as a discretecomponent separate from RF transistor 210 or can be integrated with RFtransistor 210 on the same die. Resistance R_(IN) and inductance L_(IN2)can be implemented as discrete components or distributed componentsseparate from the RF transistor 210 or can be integrated with the RFtransistor 210 on the same die. In one embodiment, resistance R_(IN) andinductance L_(IN2) provide input match compensation for the parasiticcapacitances of RF transistor 210 including, but not limited to, thegate (G) to source (S) capacitance of RF transistor 210. The input matchnetwork 220 can have other configurations which are within the scope ofthe embodiments described herein.

Input match network 220 provides a low impedance at the gate (G) of RFtransistor 210 over the baseband frequency range, e.g., between 0 to 300MHz, and reduces a gain response peak within this frequency range, whichmay result in lower peak voltages at the drain (D) of RF transistor 210.Input match network 220 provides an impedance match between terminal(IN) and a gate (G) of RF transistor 210 over a range of signalfrequencies that are amplified by power circuit 200. In otherembodiments, input match network 220 provides an impedance match betweenterminal (IN) and a gate (G) of RF transistor 210 over at least aportion of a range of signal frequencies that are amplified by powercircuit 200. In one embodiment, the range of signal frequencies that areamplified by power circuit 200 are in the 1 to 3 GHz range. In anotherembodiment, the range of signal frequencies that are amplified by powercircuit 200 are in the 400 MHz to 4 GHz range.

The values of resistor R_(IN) and inductor L_(IN2) are selected tocreate a match between an input impedance of RF transistor 210 andimpedance at the terminal (IN) of power circuit 200. Within the range ofsignal frequencies that are in the 400 MHz to 4 GHz range, the value ofcapacitor C_(IN) has a substantially negligible contribution to theimpedance match. The value of capacitor C_(IN) is selected so that theseries combination of resistor R_(IN), inductor L_(IN2) and capacitorC_(IN) substantially reduces the magnitude of the impedance presented tothe gate (G) of RF transistor 210 over the baseband frequency range. Inother embodiments, for different applications, the baseband frequencyrange can include frequencies that are greater than 300 MHz, and the RFsignal bandwidth or RF region for signals that are amplified by powercircuit 200 can include frequencies that are lower than 400 MHz orfrequencies that are greater than 4 GHz. In the embodiment illustratedin FIG. 2, C_(IN)=2 nF, R_(IN)=0.3 ohms and L_(IN)2=70 pH. Because thecapacitance value of C_(IN) used in input match network 220 may dependon the application in which the power circuit 200 is used, in otherembodiments, capacitor C_(IN) can have other suitable values.

FIG. 3 illustrates a baseband impedance presented to gate (G) of RFtransistor 110/210 as a function of frequency and respectively withinput match networks 120/220. Curve 310 illustrates the impedance atgate (G) of RF transistor 110 for power circuit 100 (refer to Z_(IN1) inFIG. 1) with conventional input match network 120. Curve 320 illustratesthe impedance at gate (G) of RF transistor 210 for power circuit 200(refer to Z_(IN2) in FIG. 2) for an embodiment of input match network220 where C_(IN) has a value of 2 nF. The terminals (IN) of powercircuits 100/200 have a characteristic impedance of 50 ohms.

Over the baseband frequency range of 0 to 300 MHz, input match network220 provides a much lower input impedance to gate (G) of RF transistor210 than conventional input match network 120 provides to gate (G) of RFtransistor 110. Curve 310 illustrates that with input match network 120,a maximum impedance is presented at gate (G) of RF transistor 110 ofabout 48 ohms (at 1 MHz). With input match network 220, curve 320illustrates that a maximum impedance is presented at gate (G) of RFtransistor 210 of about 6 ohms (at 1 MHz).

Overall the maximum impedance presented to gate (G) of RF transistor110/210, over the low-frequency range, in comparison to thecharacteristic input impedance at terminal (IN) of power circuits100/200 is much lower with input match network 220 than with input matchnetwork 120. In the illustrated embodiment, for a 100 W RF powertransistor, a ratio of the magnitude of impedance Z_(IN2) presented togate (G) of RF transistor 210 to the source impedance of 50 ohms forpower circuit 200 ranges from approximately 0.02 to 0.12 over a 1 to 300MHz frequency range. In other embodiments, the ratio of the magnitude ofimpedance Z_(IN2) presented to gate (G) of RF transistor 210 to thesource impedance of 50 ohms for power circuit 200 has a maximum value of0.4 over the 1 to 300 MHz frequency range. In other embodiments, a ratioof the magnitude of impedance Z_(IN2) presented to gate (G) of RFtransistor 210 to the source impedance of 50 ohms for power circuit 200ranges from approximately 0.02 to 0.4 over a 1 to 300 MHz frequencyrange.

The input match network 220 provides an impedance match between terminal(IN) and gate (G) of RF transistor 210 at the intended RF operatingfrequency, which is approximately 2 GHz in this illustration, and thevalue of capacitor C_(IN) has a substantially negligible contribution tothe impedance match. As FIG. 3 illustrates, beginning at 1 GHz, theimpedances presented to gate (G) of RF transistors 110/210 by inputmatch networks 120/220 are approximately equivalent. The value ofcapacitor C_(IN) is selected so that the series combination of resistorR_(IN), inductor L_(IN2) and capacitor C_(IN) substantially reduce themagnitude of the impedance presented to the input of RF transistor 210over the baseband frequency range at the terminal (IN) of power circuit200. Curve 320 illustrates that with input match network 220, a maximumimpedance is presented to gate (G) of RF transistor 210 of about 6 ohms(at 1 MHz) which is significantly lower than the source impedance of 50ohms at the terminal (IN) of power circuit 200. In other embodiments, amaximum impedance presented to gate (G) of RF transistor 210 is equal toor less than 20 ohms in the low frequency region. This is illustrated inFIG. 3. In other embodiments, the maximum impedance presented to gate(G) of RF transistor 210 is equal to or less than 20 ohms forfrequencies ranging from 1 MHz up to at least one-third of the intendedRF operating frequency. Note that curve 310 shows an impedance magnitudethat is close to 50 ohms over the low-frequency range. This indicatesthat the conventional matching circuit, which is a low pass circuit, ishaving little or no effect on signals in the low-frequency region. For alarger device, for instance a 200 W RF transistor, the maximum impedancepresented to the gate of the transistor in the low frequency region maybe approximately 10 ohms. Similarly, for a 50 W RF transistor, themaximum impedance presented to the gate of the transistor in the lowfrequency region may be approximately 40 ohms.

FIGS. 4 and 5 illustrate the gain response (dB) of power circuit 200 asa function of the value of blocking capacitor C_(IN) and frequency. FIG.4 illustrates a frequency range from 0 to 700 MHz which includes the lowfrequency baseband range of 1 to 300 MHz. FIG. 5 illustrates a frequencyrange from 0 to 3 GHz which includes both the baseband frequency rangeand the RF region of operation. Referring to FIG. 4, curve 410represents a blocking capacitor C_(IN) value of 100 pF, curve 420represents a blocking capacitor C_(IN) value of 500 pF, curve 430represents a blocking capacitor C_(IN) value of 1.2 nF, and curve 440represents a blocking capacitor C_(IN) value of 2 nF. Referring to FIG.5, curve 510 represents a blocking capacitor C_(IN) value of 100 pF,curve 520 represents a blocking capacitor C_(IN) value of 500 pF, curve530 represents a blocking capacitor C_(IN) value of 1.2 nF, and curve540 represents a blocking capacitor C_(IN) value of 2 nF. Referring toFIG. 4 and FIG. 5, for capacitor C_(IN) values of 100 pF (curve 410/510)and 2 nF (curve 440/540), for increasing values of C_(IN) the gain andcorresponding gain peak in the baseband range is significantly reducedwhile the impact of the value of C_(IN) on the gain at the intended RFoperating frequency, which is approximately 2 GHz, is much lower andbecomes increasingly negligible at higher frequencies.

For a capacitor C_(IN) value of 2 nF (curve 440/540), the gain responsepeak in the low frequency baseband range of 0 to 300 MHz (see FIG. 4) isabout −12 dB while the gain response at the approximate intended RFoperating frequency, which is approximately 2 GHz, is about 23 dB. Thedifference between the gain response peak in the low frequency basebandrange and the gain response at the approximate intended RF operatingfrequency, which for this embodiment is approximately 2 GHz, is about 35dB for a capacitor C_(IN) value of 2 nF. For a capacitor C_(IN) value of1.2 nF (curve 430/530), the gain response peak in the low frequencybaseband range of 0 to 300 MHz (see FIG. 4) is about −12 dB while thegain response at the approximate intended RF operating frequency, whichis approximately 2 GHz, is about 23 dB. The difference between the gainresponse peak in the low frequency baseband range and the gain responsein the approximate center of the high frequency RF region for acapacitor C_(IN) value of 1.2 nF is about 35 dB. For capacitor C_(IN)values of 2.0 nF and 1.2 nF, the gain response peak reduction in the lowfrequency baseband range has resulted in a difference between the gainresponse peak in the low frequency baseband range and the gain responseat the approximate intended RF operating frequency of about 35 dB. Inanother embodiment, the difference between the gain response peak in thelow frequency baseband range and the gain response at the intended RFoperating frequency is about 28 dB. In other embodiments, the highfrequency RF region and the intended RF operating frequency can be inthe 400 MHz to 4 GHz range. The RF region and the intended RF operatingfrequency for different applications can be lower or higher than theaforementioned range. Furthermore, the low frequency baseband range fordifferent applications can extend to frequencies that are greater than300 MHz.

FIG. 6 illustrates measured results of the gain response of conventionalpower circuit 100 and an embodiment of power circuit 200 in the basebandfrequency range of 0 to 400 MHz. Curve 610 illustrates the gain responsefor power circuit 100 and curve 620 illustrates the gain response forpower circuit 200. In this embodiment of power circuit 200, input matchcircuit 220 has a blocking capacitor C_(IN) value of 2 nF. Forconventional power circuit 100, curve 610 illustrates a gain peak of −2dB at 217 MHz (refer to m1). For the illustrated embodiment of powercircuit 200, curve 620 illustrates a gain peak of −15 dB at 235 MHz(refer to m2). Compared to power circuit 100, power circuit 200 reducesthe gain in the baseband region from −2 dB to −15 dB and increases thefrequency at which the gain peak occurs from 217 MHz to 235 MHz. Such areduction in gain peak results in improved DPD system performance forpower circuit 200 and improved ruggedness for RF transistor 210.

FIG. 7 illustrates another embodiment of a power circuit 300. The powercircuit 300 shown in FIG. 7 is similar to the power circuit 200 shown inFIG. 2. Different than the power circuit 200 shown in FIG. 2, the inputmatch network 220 of the power circuit 300 shown in FIG. 7 furtherincludes a bypass capacitor C_(bypass) connected in parallel with theblocking capacitor C_(IN) and the resistor R_(IN) of the input matchnetwork 220. The input match network 220 enables broader RF bandwidthfor the power circuit 300 and tailors the low frequency (baseband)response of the RF transistor 210 as previously explained herein.However, the resistor R_(IN) of the input match network 220 can causeslight matching losses over the RF region for signals that are amplifiedby the power circuit 300. Such matching losses reduce the RF gain of thepower circuit 300 if unmitigated.

The bypass capacitor C_(bypass) connected in parallel with the blockingcapacitor C_(IN) and the resistor R_(IN) of the input match network 220provides an RF bypass path around the resistor R_(IN) over at least aportion of the high frequency (RF) region for signals that are amplifiedby power circuit 300, effectively removing the resistor R_(IN) over atleast a portion of the RF region of interest. According to thisembodiment, the resistor R_(IN) of the input match network 220 has noadverse effect on the gain of the power circuit 300 over at least aportion of the RF signal region but is available (i.e. not bypassed)over the low frequency baseband region to advantageously tailor thebaseband characteristics of the power circuit 300 as previouslydescribed herein.

FIG. 8 illustrates yet another embodiment of a power circuit 400. Thepower circuit 400 shown in FIG. 8 is similar to the power circuit 300shown in FIG. 7. Different than the power circuit 300 shown in FIG. 7,the bypass capacitor C_(bypass) is connected in parallel with only theresistor R_(IN) of the input match network 220. This way, the physicalsize of the bypass capacitor C_(bypass) can be reduced since it is notdirectly connected to ground.

In either case, the blocking capacitor C_(IN) of the input match network220 is a high value capacitor that provides a low impedance path to theRF signal envelope. In one embodiment, the blocking capacitor C_(IN) isin the nF range e.g. multiples of nF in value. The bypass capacitorC_(bypass) of the input match network 220 is a bypass capacitor thatbypasses the resistor R_(IN) of the input match network 220 over atleast a portion of the RF region for signals that are amplified andreduces matching losses caused by the resistor R_(IN). In oneembodiment, the bypass capacitor C_(bypass) is in the pF range e.g.multiples of pF in value. The resistor R_(IN) of the input match network220 can be in the milliohm range e.g. multiples of milliohms in value,and the inductor L_(IN2) of the input match network 220 can be in the pHrange e.g. multiples of pH in value. The components L_(IN2), R_(IN),C_(IN), and C_(bypass) of the input match network 220 can be integratedon a single semiconductor IC such as a silicon IC or other type ofsemiconductor IC.

Spatially relative terms such as “under”, “below”, “lower”, “over”,“upper” and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first”, “second”, and the like, are also used to describevarious elements, regions, sections, etc. and are also not intended tobe limiting. Like terms refer to like elements throughout thedescription.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

With the above range of variations and applications in mind, it shouldbe understood that the present invention is not limited by the foregoingdescription, nor is it limited by the accompanying drawings. Instead,the present invention is limited only by the following claims and theirlegal equivalents.

What is claimed is:
 1. A power circuit, comprising: an RF transistor; aninput match network coupled to an input to the RF transistor and to aninput to the power circuit, the input match network including aresistor, an inductor and a first capacitor coupled together in seriesbetween the input to the RF transistor and a ground, and a secondcapacitor coupled in parallel with at least the resistor, wherein thevalues of the resistor and the inductor are selected to match an inputimpedance of the RF transistor to a source impedance at the input of thepower circuit over at least a portion of a high frequency range, whereinthe value of the first capacitor is selected so that the seriescombination of the resistor, the inductor and the first capacitor reducethe magnitude of the impedance presented to the input of the RFtransistor in a low frequency range relative to the source impedance atthe input of the power circuit, wherein the value of the secondcapacitor is selected so that the resistor is bypassed over at least aportion of the high frequency range.
 2. The power circuit of claim 1,wherein the low frequency range is from about 0 to about 300 MHz.
 3. Thepower circuit of claim 1, wherein the high frequency range is from about400 MHz to about 4 GHz.
 4. The power circuit of claim 1, furthercomprising: an output match network coupled to an output of the RFtransistor and to an output to the power circuit, wherein a differencebetween a gain response peak in the baseband range and a gain responseat an intended RF operating frequency for the power circuit is equal toor greater than 28 dB.
 5. The power circuit of claim 1, wherein a ratioof the magnitude of the impedance presented to the input of the RFtransistor to the source impedance at the input of the power circuitover a 1 to 300 MHz frequency range is equal to or less than 0.4.
 6. Thepower circuit of claim 1, wherein a ratio of the magnitude of theimpedance presented to the input of the RF transistor to the sourceimpedance at the input of the power circuit over a 1 to 300 MHzfrequency range is between about 0.02 and about 0.4.
 7. The powercircuit of claim 1, wherein the magnitude of the impedance presented tothe input of the RF transistor is equal to or less than 20 ohms forfrequencies ranging from 1 MHz up to at least one-third of an intendedRF operating frequency.
 8. The power circuit of claim 1, wherein the RFtransistor is a MOS transistor.
 9. The power circuit of claim 1, whereinthe RF transistor is a LDMOS transistor.
 10. The power circuit of claim1, wherein the RF transistor is a GaN MESFET transistor.
 11. The powercircuit of claim 1, wherein the value of the first capacitor is in thenF range and the value of the second capacitor is in the pF range. 12.The power circuit of claim 1, wherein the second capacitor is coupled inparallel with only the resistor.
 13. The power circuit of claim 1,wherein the second capacitor is coupled in parallel with the resistorand the first capacitor.
 14. An RF power amplifier, comprising: an inputconfigured to receive a RF signal having a RF signal bandwidth; a LDMOStransistor configured to amplify the RF signal; an input match networkcoupled to the input of the RF power amplifier and a gate of the LDMOStransistor, the input match network including a resistor, an inductorand a first capacitor coupled together in series between the input ofthe RF power amplifier and a ground, and a second capacitor coupled inparallel with at least the resistor, wherein the values of the resistorand the inductor are selected to match an impedance at the gate of theLDMOS transistor to a source impedance at the input of the RF poweramplifier over at least a portion of the RF signal bandwidth, whereinthe value of the first capacitor is selected so that the input matchnetwork substantially reduces the magnitude of the impedance presentedto the gate of the LDMOS transistor in a baseband frequency rangerelative to the source impedance at the input of the RF power amplifier,wherein the value of the second capacitor is selected so that theresistor is bypassed over at least a portion of the RF signal bandwidth.15. The RF power amplifier of claim 14, wherein the baseband frequencyrange is from about 0 to about 300 MHz.
 16. The RF power amplifier ofclaim 14, wherein the RF signal bandwidth is from about 400 MHz to about4 GHz.
 17. The RF power amplifier of claim 14, wherein the value of thefirst capacitor is in the nF range and the value of the second capacitoris in the pF range.
 18. The RF power amplifier of claim 14, wherein thesecond capacitor is coupled in parallel with only the resistor.
 19. TheRF power amplifier of claim 14, wherein the second capacitor is coupledin parallel with the resistor and the first capacitor.
 20. A powercircuit, comprising: an RF transistor; an input match network coupled toan input to the RF transistor and to an input to the power circuit, theinput match network including a resistor, an inductor and a firstcapacitor coupled together in series between the input to the RFtransistor and a ground, and a second capacitor coupled in parallel withat least the resistor, wherein the value of the resistor is in themilliohm range, the value of the inductor is in the pH range, the valueof the first capacitor is in the nF range, and the value of the secondcapacitor is in the pF range.